Field of the Invention
The present disclosure generally relates to optical illumination systems are more specifically relates to the use of amplitude modulation spatial light modulators in combination with phase modulation spatial light modulators in an optical illumination system.
Related Art
One conventional means to create spatial light patterns is to modulate the amplitude of light as a function of position within a two dimensional plane. Examples of such conventional means include traditional film projection, liquid crystal display (“LCD”) projectors, and digital micromirror device (“DMD”) based projectors. DMD devices are reflective devices that can project very high intensities of light and can be very rapidly switched. A fundamental limitation of DMD devices is that they are extremely inefficient at utilizing the available light energy when only a small portion of the target area (e.g., a sample) needs to be illuminated. This is particularly problematic if small localized regions of the sample require very high light intensities, such as during photolysis of caged compound and stimulation for optogenetics. In addition, DMD devices embody a fundamentally two dimensional technology and cannot simultaneously control light in three dimensions.
An alternate conventional means to create spatial light patterns is to modulate the phase of the light. An example of this conventional means includes holography. Fundamental limitations of digital holographic systems include the production of zero and higher order diffraction patterns as well as ghost images that must be blocked. Typically, a static physical barrier is used to block the zero order diffraction pattern. Currently, there are no practical solutions to block the higher order diffraction patterns and ghost images and in many circumstances these extraneous patterns are unacceptable. In addition, most phase only spatial light modulators (“SLMs”) are unable to rapidly switch between different patterns. Moreover, the diffraction efficiency and therefore the distribution of light in the field of view of the objective lens depend on the lateral position. In most applications for patterned illumination it is desirable to have a flat field in terms of intensity as a function of space.
Yet another alternate conventional means for creating spatial light patterns is to sequentially scan a series of points rapidly as is currently done with confocal laser scanning microscopy and two-photon microscopy. This means is problematic because the speed of scanning is insufficient and is further problematic due to limitations related to how much power any single spot on the sample can tolerate.
Therefore, what is needed are systems and methods that overcome these significant problems found in the conventional systems as described above.